Cutting tools and rock drilling tools used during subterranean drilling operations, such as operations for drilling boreholes into the earth for the recovery of hydrocarbons (e.g., oil and natural gas), typically include a bit body and a plurality of cutting elements disposed on the bit body. These cutting elements commonly incorporate ultra-hard materials, such as polycrystalline diamond (PCD), due to their good wear resistance and hardness properties. Additionally, the PCD bodies are commonly bonded or otherwise coupled to substrates. The substrates facilitate attachment of the cutting elements to the bit body, such as by brazing.
PCD bodies are conventionally formed by sintering diamond particles mixed with a catalyst material, such as a metal catalyst selected from Group VIII of the periodic table, at high pressure and high temperature (HPHT). During the HPHT sintering process, the diamond particles form into an interconnected network of diamond crystals and the catalyst material infiltrates and occupies interstitial spaces or pores between the bonded diamond crystals. However, conventional PCD bodies are prone to thermal degradation because the catalyst material has a higher coefficient of thermal expansion than the diamond crystals. In particular, the thermal expansion differential between the catalyst and the diamond crystals and catalyst interstitially disposed between the diamond crystals can induce thermal stresses in the and the formation of cracks in the PCD body when the cutting element is subject to elevated temperatures, such as during a drilling operation. These thermal stresses may eventually result in the formation of cracks in the PCD body and the premature failure of the cutting element.
Accordingly, a variety of techniques have been developed to produce thermally stable PCD (TSP). Conventional processes for forming TSP bodies include using a non-metal catalyst during the HPHT sintering process of the diamond particles, HPHT sintering diamond particles without the use of a catalyst, or leaching a conventional PCD body with an acid to remove at least a portion of the catalyst material formed in the interstitial regions between the bonded diamond crystals.
Additionally, pre-formed TSP bodies may be joined to the substrates by placing the TSP body in a mold and then filling a remainder of the mold with a material configured to form the substrate when subject to elevated temperatures. The material configured to form the substrate typically includes a matrix material, such as tungsten or tungsten carbide, and a binder material, such as cobalt. When the mold is heated, the binder material is configured to infiltrate the matrix material and thereby bind the matrix particles together to form the substrate. Additionally, the binder material is configured to join the substrate to the TSP body by wetting the interface surface between the TSP body and the substrate and filling the pores between the diamond particles in the TSP body along the interface surface.